Aromatic polycarbonate resins are well known and are accepted as suitable for a wide variety of uses including injection molding, extrusion and film formation. The chemistry, synthesis, properties, and applications of these polycarbonates are extensively discussed in Chemistry and Physics of Polycarbonates by Schnell, Interscience, 1964 and Polycarbonates by Christopher and Fox, Reinhold, 1962.
Although polycarbonates have some inherent flame resistance, being self-extringuishing, ever more demanding flame retardancy requirements have spawned numerous attempts to increase this property. Among the methods to improve the flame retardance there is noted adding substantial amounts of halogen to polycarbonate resins such as by employing a halogen substituent on the polycarbonate polymer chain (U.S. Patent 3,751,400 and 3,334,154) or adding a monomeric halogenated compound as in U.S. Patent 3,382,207. Also noted, is the approach taguth by U.S. Patent 3,775,367 which entails adding an organic and/or inorganic metal salt to the composition. Additions of perfluoroalkane sulfonic acid salts of alkali metals and organic alkali salts of carboxylic acids have been disclosed in U.S. Patent 3,836,490 and in U.S. Patent 3,775,367. Also noted is German Published Patent No. 2,149,311 which discloses the use of insoluble alkali metal salts, particularly salts of inorganic acids, phosphonic acids and sulphonic acids. Flame rtardant polycarbonate compositions containing alkali metal salts of an inorganic acid are disclosed in U.S. patent 4,223,100. U.S. Patent 3,535,300 discloses the use of small amounts of specified metal salts (which do not include alkali metal salts) in combination with halogen carried on the polymeric backbone or on an additive. U.S. Patent 4,110,299 teaches adding of alkali or alkaline earth metal salts of organic acids in combination with additives such as inorganic halide and an organic monomeric or polyermic aromatic or heterocyclic halide improve the flame retardancy of an aromatic polycarbonate.
Also noted are the teachings in regard to the drip suppression of the compositions when they are exposed to a flame. In German Patent No. 2,535,262 there is a teaching to add fluorinated polyolefins such as polytetrafluoroethylene (PTFE) to a polycarbonate containing organic alkal imetal salt to retard dripping. U.S. Patent 4,110,299 discloses adding to a polycarobnate resin fluorinated polyolefin, fibrous glass or a siloxane, in combination with certain salts and an inorganic halide to diminish tendency to drip. In PCT application WO 80/00084 there is disclosed--in Example 13--a blend of aromatic polycarbonate and a block copolymer of polycarbonate and polydimethylsiloxane (57%/43%) and including sodium salt of trichloro benzene sulfonic acid. The blend was noted to have improved resistance to stress crazing. The document generally discloses improved ductility, solvent resistance and flame retardance characteristics of blends of polycarbonates and a block copolymer of polycarbonate and polydiorganosiloxane.
Polydiorganosiloxane copolycarbonates of the type entailed in the present invention are known.